DE69701248T2 - Permeable adhesive tape and process for its manufacture - Google Patents

Description

BACKGROUND OF THE INVENTION

The present invention relates to a permeable adhesive tape and a method for its production, in particular to a permeable adhesive tape which can be wound up in a roll and whose permeability does not or hardly deteriorates over time, and a method for its production.

Description of the related art

Commonly used adhesive tapes, such as adhesive plasters, bandages and surgical drapes, adhere to the skin during use. If they are adhered and held to the skin for a long time, the adhesive tapes may cause a rash, eruption or maceration of the skin. To avoid this difficulty, it is desirable that the adhesive tapes have permeability.

U.S. Patent No. 4,789,413 describes a method for producing an adhesive tape having permeability, the method comprising dispersing a water-absorbent high molecular substance containing water uniformly in a rubber base or in an adhesive solution for an acrylic pressure-sensitive adhesive in an organic solvent, applying this dispersion to a release sheet, followed by drying, and then laminating a porous backing to the surface to which the dispersion has been applied.

Generally, the adhesive tape is wound onto a rod core in the form of a roll when manufactured in a factory and then stored or shipped in the form of the roll before being processed into the desired shape.

Usually, the tape wound on a roll suffers considerable winding pressure. (Here, winding pressure means a force applied to the adhesive tape wound on a rod core in a roll.) In particular, the winding pressure is considerably high around the inside of the roll. This winding pressure can fluidize the pressure-sensitive adhesive in the adhesive tape, thereby filling the permeable pores of the adhesive tape most prominently around the center of the roll. The adhesive tape thus gradually loses its permeability over time. After aging, the adhesive tape is cut to the width of the desired product and also wound into a small roll called a product roll for convenient storage. Since the tape in the form of the product roll also suffers winding pressure, it is impossible to avoid the deterioration of permeability over time even in the product roll.

To avoid or reduce the deterioration of permeability, it is known to fill a paper tube (a core) with a polyethylene foam or a similar material and to wind the adhesive tape on the paper tube so that the winding pressure is relaxed. It is also known to wind the adhesive tape less tightly with a controlled winding tension.

However, in the former way, the polyethylene foam must be made thick enough to relax the winding pressure, and the thick foam may cause deformation of the tape. In the latter way, the loosely wound roll may easily lose its shape.

It is also known from U.S. Patent No. 5,198,064 to incorporate hydrophobic inorganic particles such as silica into the pressure-sensitive adhesive layer. However, the hydrophobic inorganic particles described in this publication are not added for the purpose of ensuring permeability, but for the purpose of preventing contact of water contained in the permeability-producing agent with a cross-linking agent added to improve adhesion of the pressure-sensitive adhesive layer. It is therefore impossible to prevent permeability from deteriorating due to winding pressure even with the addition of the hydrophobic inorganic particles.

It is further known from Japanese Unexamined Patent Publication (Kokai) No. Hei 2(1990)-45582 to apply an adhesive liquid containing hollow microspheres to the permeable base having pores with an average pore diameter of 1 to 50 µm, and to partially remove the self-adhesive liquid by blowing gas or sucking air through the pores of the permeable base so that a permeable adhesive layer containing pores is formed. However, the size of the pores obtained by blowing gas or sucking air is generally small in comparison with the pores of the permeable base, and therefore sufficient permeability cannot be obtained in the adhesive layer. When pores are formed by blowing gas, the surface of the adhesive layer is roughened. On the other hand, in case the pores are formed by sucking air, the adhesive liquid flows out onto the surface of the permeable bottom opposite to the surface where the adhesive was applied.

SUMMARY OF THE INVENTION

Due to the above difficulties, the present invention relates to a permeable adhesive tape comprising a porous or permeable backing, a pressure-sensitive adhesive layer of natural rubber base, synthetic rubber base, or acrylic base, and a release sheet in that order, wherein the pressure-sensitive adhesive layer has permeable pores containing elastic microspheres.

The invention further relates to a process for producing a permeable adhesive tape comprising the dispersion of non-hollow elastic microspheres, hollow elastic microspheres or expandable microspheres homogeneously in a permeable activity-generating agent to form a first dispersion, dispersing the first dispersion in a solution of a pressure-sensitive adhesive to which a crosslinking agent is optionally added; applying the second dispersion to a release liner to form a second dispersion, followed by drying while converting the expandable microspheres, if used, into hollow elastic microspheres, the pressure-sensitive adhesive layer having permeable pores containing non-hollow elastic microspheres or hollow elastic microspheres, and then laminating a porous backing or a permeable backing to the pressure-sensitive adhesive layer.

The invention further relates to a method for producing a permeable adhesive tape comprising homogeneously dispersing non-hollow elastic microspheres, hollow elastic microspheres or expandable microspheres in a system in which a permeability-imparting agent and optionally a crosslinking agent are homogeneously dispersed in a solution of a pressure-sensitive adhesive, applying the dispersion to a release paper, followed by drying while converting the expandable microspheres, if used, into hollow elastic microspheres, thereby forming a pressure-sensitive adhesive layer having permeable pores containing non-hollow elastic microspheres or hollow elastic microspheres, and then laminating a porous backing or a permeable backing onto the pressure-sensitive adhesive layer.

DESCRIPTION OF PREFERRED EMBODIMENTS

The above and other objects, features and advantages of the present invention will be more fully understood from the following description.

As the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer, natural rubber-based adhesives, synthetic rubber-based adhesives and acrylic adhesives can be used. The adhesives can be suitably selected from those used in the field. Particularly, reference is made to a pressure-sensitive adhesive as described in U.S. Patent No. 4,789,413. Furthermore, a tackifier, a plasticizer, an antioxidant and a preservative can be added, and a single agent or a mixture of two or more of them can be added.

The pressure-sensitive adhesive layer may preferably be 2 to 100 µm thick after drying. More preferably, it is 35 to 75 µm thick after drying. A number of permeable pores are formed in the pressure-sensitive adhesive layer. The term "permeable" as used in the present invention means the characteristic feature that it can be permeated by gases such as air and water vapor. The degree of permeability is represented by a value determined according to JIS (Japanese Industrial Standard) L-1099-1993 A-2 (water) test. The size of the permeable pores is such that the pores in one surface and the opposite surface of the pressure-sensitive adhesive layer can communicate.

According to the invention, the pressure-sensitive adhesive layer has permeability, and a part or all of the permeable pores thereof contain elastic microspheres to such an extent that the elastic microspheres do not hinder the permeability.

As elastic microspheres, either non-hollow elastic microspheres or hollow elastic microspheres can be used.

Examples of materials for non-hollow elastic microspheres include urethane polymers, acrylic rubbers such as copolymers of ethyl acrylate and chloroethyl vinyl ether, copolymers of n-butyl acrylate and acrylonitrile and copolymers of acrylic acrylate and acrylonitrile, and urethane-modified acrylic rubbers.

Examples of materials for the hollow elastic microspheres include cross-linked styrene polymers, styrene-acrylonitrile copolymers, polymers such as methyl methacrylate-acrylonitrile, and vinylidene chloride-acrylonitrile.

The diameter of the elastic microspheres is, for example, 10 to 100 µm, preferably 15 to 80 µm, as an average particle diameter. According to the present invention, it is preferable that the elastic microspheres are present at least in permeable pores, but the elastic microspheres may also be present in other parts of the pressure-sensitive adhesive layer other than the permeable pores. The elastic microspheres may preferably be used in a ratio of 0.01 to 5.0 parts by weight per 100 parts by weight of the pressure-sensitive adhesive (in terms of solid content). If the elastic microspheres are used in a ratio below 0.01 part by weight, it is not preferable because the obtained permeable adhesive tape does not maintain sufficient permeability. When the elastic microspheres are used in a ratio exceeding 5.0 parts by weight, it is not preferable because sufficient adhesion cannot be obtained. The particularly preferable use ratio of the elastic microspheres is 0.1 to 3.0 parts by weight.

When the hollow elastic microspheres are used, it is preferred that the microspheres are expanded. For example, the hollow elastic microspheres more preferably have an expansion ratio of 20 to 70 times (by volume) and are solvent resistant. As discussed in the following description of the manufacturing methods, the hollow elastic microspheres described above can also be manufactured by expanding expandable microspheres during manufacture of the permeable adhesive tape.

The term "elastic" as used in the present invention means that when a pressure of 200 kg/cm2 is applied to water in which the microspheres are dispersed, the volume of the microspheres is recovered by more than 90% after the pressure is released.

The permeable pores in the pressure-sensitive adhesive layer are formed by evaporation of the water contained in the water-absorbent high molecular substance, which the pressure-sensitive adhesive solution during the preparation of the pressure-sensitive adhesive layer. The water-absorbent high molecular substance is one of those which are insoluble in water but which swells to several hundred to a thousand times its own weight by absorbing water, and the swollen substance no longer releases the absorbed water even under pressure. Examples of such water-absorptive high molecular substances include starch polymers such as starch-acrylonitrile graft polymer, starch-acrylic acid graft polymer, starch-styrenesulfonic acid graft polymer and starch-vinylsulfonic acid graft polymer, cellulose polymers such as a cellulose-acrylonitrile graft polymer, a cellulose-styrenesulfonic acid graft polymer and a cross-linked carboxymethylcellulose polymer, polyvinyl alcohol polymers such as cross-linked polyvinyl alcohol polymer, a saponified polyacrylic-vinyl acetate polymer, acrylic polymers such as cross-linked polyacrylate polymer (a cross-linked sodium acrylate polymer, a cross-linked acrylic acid-sodium acrylate polymer) and a saponified acrylonitrile polymer, polyethylene oxide polymers such as a cross-linked ethylene glycol diacrylate polymer, other polymers having a carboxyl group, carboxylate, hydroxy group and/or sulfonate and a cross-linked polyvinylpyrrolidone polymer. Specific examples are AP-300, AP-200 and AP-100 of AQUARESERVE series (crosslinked acrylic acid sodium acrylate copolymers manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), AQUARIC CA series (crosslinked sodium acrylate polymers manufactured by Nippon Shokubai Co., Ltd.) and SANWET IM-1006MPS (sodium salt of starch-acrylic acid graft polymer manufactured by Sanyo Chemical Industries, Ltd.). These water-absorptive high molecular substances are used together with water as discussed in the following explanation of the manufacturing methods, and the amount thereof is preferably 1/3000 to 1/10 part by weight, particularly preferably 1/600 to 1/20 part by weight, based on one part by weight of water. The water-absorptive high molecular substances are preferably in the form of particles or granules which can be easily dispersed in water in such forms. The particle diameter is suitably 60 µm or less, preferably 40 µm or less.

The release film or release sheet is appropriately selected from those commonly used in the field. Examples of release films are silicone-coated films and silicone-coated films. The thickness of the release sheet is not particularly limited as long as it can be used industrially in a conventional manner.

The porous or permeable base may be suitably selected from those used in the field. Examples of porous or permeable bases are woven and nonwoven cloth, a synthetic resin product with coarse mesh, a permeable polymer expanded sheet, and a permeable polymer film. The permeable base may be a non-porous base as long as it exhibits permeability.

The permeable pores in the pressure-sensitive adhesive layer, which give the permeable adhesive tape of the present invention, are formed using a permeability-imparting agent as described below. For this reason, the permeable pores in the pressure-sensitive adhesive layer are not formed depending on the size and number of pores present in the porous or permeable backing. In other words, the permeable pores can be formed to give the desired permeability of the pressure-sensitive adhesive layer whether the backing is porous or non-porous.

The permeable adhesive tape according to the invention can be produced by various methods, for example according to the following methods (1) and (2):

(1) Non-hollow elastic microspheres, hollow elastic microspheres or expandable microspheres are homogeneously dispersed in a permeability-imparting agent to prepare a first dispersion. The first dispersion is dispersed in a solution of a pressure-sensitive adhesive to which a crosslinking agent has been optionally added to prepare a second dispersion. The second dispersion is coated on a release liner, followed by drying while the expandable microspheres, if used, are converted into hollow elastic microspheres, thereby forming a pressure-sensitive adhesive layer containing permeable pores containing non-hollow elastic microspheres or hollow elastic microspheres. Then, a porous back layer or a permeable back layer is laminated on the pressure-sensitive adhesive layer.

(2) Non-hollow elastic microspheres, hollow elastic microspheres or expandable microspheres are homogeneously expanded in a system in which a permeability-imparting agent and optionally a cross-linking agent are homogeneously dispersed in a solution of the pressure-sensitive adhesive. The dispersion is applied to a release paper, followed by drying while the expandable microspheres, if used, are converted into hollow elastic microspheres, thereby forming the pressure-sensitive adhesive layer having permeable pores containing non-hollow elastic microspheres or hollow elastic microspheres. Then, a porous bottom surface or a permeable bottom surface is laminated to the pressure-sensitive adhesive layer.

The above procedure (1) will now be explained in more detail.

First, non-hollow elastic microspheres, hollow elastic microspheres or expandable microspheres are homogeneously dispersed in a permeability-imparting agent to form a first dispersion. The term "homogeneous" is not used in the present invention in a strict sense, but in such a sense as to include substantial homogeneity, and this applies throughout the description of the present invention.

One can use any permeability imparting agent which creates permeable pores by evaporation of water contained in it during the following drying step. fe. Preferred as the permeability-imparting agent is a water-absorbent high molecular substance containing water. The amount of the permeability-imparting agent is preferably 5 to 100 parts by weight per 100 parts by weight of the pressure-sensitive adhesive solution. The amount of the permeability-imparting agent used is preferably 10 to 40 parts by weight based on the rubber-based pressure-sensitive adhesive, and 20 to 100 parts by weight, more preferably 25 to 75 parts by weight, and particularly preferably 30 to 70 parts by weight in the case of an acrylic pressure-sensitive adhesive.

Examples of non-hollow elastic microspheres include non-hollow elastic microspheres made of urethane polymer such as ARTPEARL C-300 manufactured by Negami, Japan and non-hollow elastic microspheres made of acrylic rubber such as ARTPEARL G-400 manufactured by the same company.

As the expandable microspheres, those which have an average particle diameter of 5 to 30 µm and expand by 20 to 70 times (by volume) to form hollow elastic microspheres in the final permeable adhesive product are preferably used. For the hollow elastic microspheres and the expandable microspheres, EXPANCEL series manufactured by Japan Fillite Co., Ltd., Japan is suitable. Particularly, EXPANCEL 091DE80 (expanded) is preferred for the hollow elastic microspheres, and EXPANCEL 642WU (its expansion temperature is 90 to 120ºC) is suitable for the expandable microspheres. F-50D manufactured by Matsumoto, Japan can also be used as the expandable microspheres. The expandable microspheres can be primarily expanded to some extent in advance. Such primary expanded hollow elastic microspheres can be added to the adhesive solution and secondarily expanded during the drying step, converting them into hollow elastic microspheres.

Water and the water absorbed in the water-absorbent macromolecular substance serves to form the permeable pores in the pressure-sensitive adhesive layer.

Then, the first dispersion is homogeneously dispersed into a solution of pressure-sensitive adhesive to which a cross-linking agent has been optionally added to form a second dispersion.

If the pressure-sensitive adhesive allows the first dispersion to be dispersed therein, the pressure-sensitive adhesive can be used as it is. If the pressure-sensitive adhesive is too viscous to allow the first dispersion to be dispersed, an organic solvent can be added as needed. Examples of usable organic solvents are ethyl acetate, toluene, hexane, xylene and acetone.

The crosslinking agent serves to improve the cohesive force of the pressure-sensitive adhesive and the retention of adhesion to a material to be adhered. Isocyanate crosslinking agents are preferred as crosslinking agents, and multifunctional isocyanate compounds having at least two isocyanate groups are more preferred. Examples of such compounds are tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), toluidine diisocyanate (TODI), xylylene diisocyanate (XDI), hexamethylene diisocyanate (HMDI), trimethylolpropane (TMP)-TDI adduct, multifunctional aromatic polyisocyanates (TDI polymers, etc.), polymethylene polyphenyl isocyanate and partially modified compounds thereof. Preferably, 0.5 to 10 parts by weight of crosslinking agent is added to 100 parts by weight of pressure-sensitive adhesive. Other crosslinking agents that can be used include those that can be used to crosslink a pressure-sensitive adhesive. Examples of such crosslinking agents are aziridine compounds, epoxy compounds, metal chelate compounds, melamine compounds and modified isocyanate compounds as described in U.S. Patent 5,198,064.

A tackifier, a plasticizer, an antioxidant, a colorant and a preservative may be added to the second dispersion.

The second dispersion is then applied to a release liner and dried to form the pressure-sensitive adhesive layer. These application and drying steps can be carried out using known techniques. For example, the drying step can use multi-zone drying using different zones that differ in temperature and air flow. When expandable microspheres are used, the expandable microspheres can be subjected to an expansion step after the drying step, but it is more preferred to carry out the drying and expansion steps simultaneously under conditions that allow both steps to occur. Such conditions vary depending on which expandable microspheres are used, but heating to 80 to 200°C for 0.5 to 5 minutes is preferred. On the other hand, when non-hollow elastic microspheres or hollow elastic microspheres are used, heating at 40 to 120°C for 1 to 10 minutes is preferred.

Then, a porous or a permeable backing is laminated to the pressure-sensitive adhesive layer to form a permeable adhesive tape.

The permeable adhesive tape is wound up as a roll or cylinder, usually with the release liner.

Next, the method (2) will be explained. This method is carried out in the same manner as the method (1) described above, except that the materials constituting the pressure-sensitive adhesive layer are homogeneously dispersed all at once.

In this context, both the adhesive tapes prepared according to the methods (1) and (2) do not lose their permeability much when subjected to the winding pressure, which is in contrast to the known permeable tapes that do not contain elastic microspheres.

It is believed that the following mechanism is the reason why the permeable adhesive tape of the present invention maintains its permeability.

The known permeable tape is subjected to a winding pressure when it is wound up as a roll, so that the pressure-sensitive adhesive layer is fluidized therefrom and flows toward the permeable pores and blocks them. This movement of the pressure-sensitive adhesive layer is particularly pronounced around the center where the winding pressure is relatively large. As the winding pressure continues to act, the permeable pores narrow and are almost blocked. Once the permeable adhesive tape has assumed such a state, the permeable adhesive tape cannot return to its original state even if the pressure is relaxed, so that the permeability deteriorates.

On the other hand, when the permeable tape of the present invention also suffers a winding pressure when it is rolled up as a roll, but the elastic microspheres are present throughout or at least in a part thereof, preferably in the inner wall thereof, the permeable pores can prevent the permeable pores from being blocked by fluidization of the pressure-sensitive adhesive layer. When the permeable adhesive layer is released from the pressure, the elastic microspheres resume their shape so that the space is secured. It is believed that this prevents or reduces the deterioration of the permeability.

In addition, the permeable adhesive tape of the present invention is preferably used for adhesive plasters, bandages and surgical pads, but its use is not limited thereto. The permeable adhesive tape of the present invention can be used where retention of permeability is required.

EXAMPLES

The following examples illustrate the invention without limiting it. In these examples, the permeability of the permeable adhesive tape is demonstrated by measuring the moisture permeability.

example 1

Non-hollow elastic microspheres of ARTPEARL C-300 (urethane polymer microspheres having an average particle diameter of 15 µm, manufactured by Negami) were used as elastic microspheres. These microspheres were homogeneously mixed with 50 parts by weight of a permeability-imparting agent (water-containing AR-739M, a water-absorptive high molecular substance, manufactured by Rikidyne, Japan) with different amounts of the microspheres used to obtain first dispersions. These first dispersions were then homogeneously mixed with 100 parts by weight of a solution of an acrylic pressure-sensitive adhesive (RIKIDYNE AR-2045, a product containing 45% by weight of solid, manufactured by Rikidyne). 5 parts by weight of modified polyisocyanate crosslinking agent (SANPASTER HD-739D, manufactured by Rikidyne) was added and mixed homogeneously to obtain second dispersions.

The above second dispersions were applied to silicone release liners according to a method for applying transfers. The amount applied was 50 g/m2/after drying. These dispersions were then dried at 105 to 120°C for 3 minutes. Permeable backing sheets made of a laminate composite of nonwoven cloth (BENLIZE CF-501, manufactured by Asahi Chemical Industry Co., Ltd., Japan) and a urethane film of 25 µm thick (Okura, Japan) were laminated. Permeable adhesive tapes were thus obtained.

The obtained permeable adhesive tapes were allowed to stand at 40°C under a load of 80 g/cm² for 3 days and 14 days. The moisture permeability of the obtained adhesive tapes was measured according to JIS L-1099 13 A-2 (water) test (expressed in g/m² for 24 hours). The measurement results are shown in Table 1 together with the adhesion strengths for each amount of the non-hollow elastic microspheres used. The adhesion strength was measured when adhesive surfaces of the tapes were contacted with a material to be bonded (glass plates), bonded by pressure by moving a rubber roller of 2 kg weight back and forth once, and immediately peeled off at an angle of 180° at a head speed of 300 mm/minute. Table I

From Table 1, it is evident that the permeable adhesive tapes containing the non-hollow elastic microspheres retain their moisture permeability, i.e., the permeability, after pressure application.

Example 2

Permeable adhesive tapes were prepared in the same manner as described in Example 1 except that ARTPEARL G-400 (acrylic rubber microspheres having an average particle diameter of 20 µm, manufactured by Negami) was used as non-hollow elastic microspheres instead of ARTPEARL C-300. The prepared permeable adhesive tapes were evaluated for moisture permeability and adhesion strength after 3 days and 14 days in the same manner as described in Example 1. The results are given in Table 2. Table 2

From Table 2, it follows that the permeable adhesive tapes containing the non-hollow elastic microspheres retain their moisture permeability, i.e., the permeability, after pressure application.

Example 3

Permeable adhesive tapes were prepared in the same manner as described in Example 1 except that hollow elastic microspheres (EXPANCEL 091DE80, about 60 times expansion, 0.03 true specific gravity, 0.020 specific bulk density, 50 to 80 µm particle diameter, manufactured by Japan Fillite Co., Ltd.) were used. The prepared permeable adhesive tapes were tested for moisture permeability and adhesion strength after 3 days and 14 days in the same manner as described in Example 1. The results are shown in Table 3. Table 3

From Table 3, it follows that the permeable adhesive tapes containing the hollow elastic microspheres maintain their moisture permeability, i.e., the permeability, after pressure application.

Example 4

Permeable adhesive tapes were prepared in the same manner as described in Example 3 except that 100 parts by weight of the solution of a rubber-based pressure-sensitive adhesive (GR-700, a natural rubber/SBR-based adhesive with a solid content of 30% by weight, manufactured by Rikidyne) and 30 parts by weight of a permeability imparting agent were used. The prepared permeable adhesive tapes were tested for moisture permeability and adhesion strength after 3 days and 14 days in the same manner as described in Example 1. The results are shown in Table 4. Table 4

From Table 4, it follows that the adhesive tapes with the rubber-based pressure-sensitive adhesive retain their moisture permeability, i.e., permeability, after the pressure application.

Example 5

Permeable adhesive tapes were prepared in the same manner as described in Example 3. However, in this example, a solution of a rubber-based pressure-sensitive adhesive (GR-700, natural rubber/SBR-based, containing 30 wt% solid, manufactured by Rikidyne) was used as the pressure-sensitive adhesive solution and expandable microspheres (F-50D, unexpanded microspheres having a particle diameter of 10 to 20 µm, manufactured by Matsumoto) were used instead of the hollow elastic microspheres. The expandable microspheres were expanded 40 times during the drying step at 115°C for 5 minutes. The prepared permeable adhesive tapes were tested for moisture permeability in the same manner as described in Example 1. The results are shown in Table 5. Table 5

It follows from Table 5 that when expandable microspheres are used as the material, the moisture permeability, i.e., the permeability of the permeable adhesive tapes, is maintained even after pressure is applied if the expandable microspheres are expanded into hollow elastic microspheres before pressure is applied.

Example 6

Monomers composed of 65 parts by weight of butyl acrylate (BA), 30 parts by weight of 2-ethylhexyl acrylate (2EHA), 2 parts by weight of acrylic acid (Aa) and 3 parts by weight of vinylpyrrolidone (NV-2P) were polymerized at 70°C for 8 hours using ethyl acetate/toluene (in a ratio of 60/40 by weight) as a solvent and 0.2 parts by weight of BPO as an initiator. In this polymerization, a polymer solution (a pressure-sensitive adhesive solution) having a solid content of 45% and a viscosity of 6500 cP (at 25°C) was obtained.

Permeable adhesive tapes were prepared in the same manner as described in Example 3 except that the above polymer solution was used in place of the acrylic pressure-sensitive adhesive solution (RIKIDYNE AR-2045, manufactured by Rikidyne). The permeable adhesive tapes prepared were measured for moisture permeability and adhesion strength after 3 days in the same manner as described in Example 1. The results are shown in Table 6. Table 6

It follows from Table 6 that when hollow elastic microspheres are used, the desired moisture permeability can be obtained even if only a relatively small amount of them is used, and that the hollow elastic microspheres are superior to the expandable microspheres in the efficiency for improving the moisture permeability.

Example 7

Hollow elastic microspheres were homogeneously dispersed in a system in which a permeability imparting agent and a crosslinking agent are homogeneously mixed with a solution of an acrylic pressure-sensitive adhesive (RIKIDYNE AR-2045, manufactured by Rikidyne) using different amounts of microspheres. Each of the resulting dispersions was applied to a release sheet and dried to form a pressure-sensitive adhesive layer. Then, a permeable composite material of laminated urethane film and nonwoven cloth as used in Example 1 was laminated on the pressure-sensitive adhesive layer to form an adhesive tape. The formed adhesive tape was tested for moisture permeability and adhesion strength under the same conditions as in Example 1 (except that the tapes were tested after being allowed to stand for 10 days). The results are shown in Table 7. In this example, the materials used for the adhesive tapes are the same as those used in Example 3. Table 7

From Table 7, it can be seen that as the amount of hollow elastic microspheres used is increased, the moisture permeability is improved more.

Example 8

The second dispersions of Example 3 were applied to silicone transfer sheets according to the method for applying transfers and dried. Then, 25 µm thick urethane films (manufactured by Okura) were laminated thereon to obtain permeable adhesive tapes. The amounts and drying conditions used were the same as described in Example 1.

The obtained permeable adhesive tapes were left to stand under the same condition as in Example 1. The moisture permeability was then measured in the same manner as described in Example 1. The results are shown in Table 8. Table 8

From Table 8, it follows that the permeable adhesive tapes without any nonwoven cloth also maintain their permeability over time.

Comparison example 1

Permeable adhesive tapes were prepared in the same manner as described in Example 1 except that a microsphere pigment (DECOSOFT WHITE 15 (trademark) having an average particle diameter of 28 µm, manufactured by CU Chemie Uetikon AG), which is a crosslinked non-elastic polyurethane-polyurea copolymer, was used instead of ARTPEARL C-300. Then, the moisture permeability was measured after 3 days and 14 days in the same manner as described in Example 1. The results are shown in Table 9. Table 9

From Table 9 it follows that the elasticity of the microspheres is important for improving and retaining moisture permeability.

Comparison example 2

The moisture permeability was measured under the same conditions as described in Example 1 except that glass microspheres [average particle diameter 22 µm, 2.47 true specific gravity, 1.73 bulk specific gravity assuming that the microspheres contain 30% air) manufactured by Nippon Ferro] were used instead of the elastic microspheres. However, the measurement was made after the tapes were allowed to stand at 40°C under a load of 80 g/cm² for 3 days. The results are shown in Table 10. Table 10

From Table 10 it follows that the elasticity of the microspheres is important in improving and retaining moisture permeability.

Comparison example 3

The moisture permeability was measured under the same conditions as described in Example 1, except that rigid microspheres of cross-linked methyl methacrylic acid polymer (non-hollow microspheres with an average particle diameter of 30 µm, a true specific gravity of 1.18 and a bulk specific gravity of 0.862, manufactured by Ganz) were used instead of the elastic microspheres. However, the measurement was made after the tapes were left to stand at 40°C under a load of 80 g/cm2 for 3 days. The results are shown in Table 11.

When rigid microspheres are used in the same volume as the elastic microspheres used in Example 1, the resulting dispersion cannot be used for coating because there is a difference in specific gravity. Table 11

It is clear from Table 11 that the moisture permeability does not improve with an increase in the amount of microspheres used. It is clear from Comparative Example 3 that the elasticity of the microspheres is important to improve the moisture permeability.

Comparison example 4

A system containing the components of the dispersion of Example 3 except the permeability-imparting agent was used. That is, hollow elastic microspheres (EXPANCEL 091DE80 with about 60-fold expansion, manufactured by Japan Fillite Co., Ltd.) or expandable microspheres (F-50D, unexpanded microspheres, manufactured by Matsumoto) were added to 100 parts by weight of acrylic pressure-sensitive adhesive (RIKIDYNE AR-2045, manufactured by Rikidyne) and 5 parts by weight of polyisocyanate crosslinking agent (SANPASTER HD-739D, manufactured by Rikidyne) in the proportions shown in Table 12 below and mixed homogeneously. These dispersions were applied to silicone release liners according to the method for applying transfers. The applied amount was 50/m2/after drying. Then, the sheets were dried at 105 to 110°C for 3 minutes in the case of the hollow elastic microspheres and at 115°C for 5 minutes in the case of the expandable microspheres. A permeable composite backing made of laminated nonwoven cloth (BENLIZE CF-501, manufactured by Asahi Chemical Industry Co., Ltd.) and 25 µm thick urethane film (manufactured by Okura) was laminated thereon to obtain permeable adhesive tapes.

The obtained permeable adhesive tapes were allowed to stand at 40°C under a load of 80 g/cm² for 3 days as described in Example 1. The moisture permeability of the permeable adhesive tapes was measured for each amount of hollow elastic microspheres used according to US L-10994₱₁₇₃₀ A-2 (water) test (expressed in g/m² for 24 hours). The results are given in Table 12. Table 12

From Table 12, it follows that when the permeability-imparting agent is not used, the moisture permeability is generally low. The moisture permeability improves somewhat with increasing the use amount of hollow elastic microspheres and expandable microspheres, but the observed moisture permeability is far from sufficient for practical use.

The permeable adhesive tape of the present invention contains elastic microspheres in all or part of the permeable pores, preferably on the inner walls of the permeable pores. Therefore, even if a winding pressure is applied to the tape when the tape is wound up as a roll, the pores are not blocked by the fluidization of the pressure-sensitive adhesive layer. When the permeable adhesive tape is released from the pressure, the elastic microspheres return to their original shape, thereby ensuring the spaces, and thus deterioration of the permeability can be prevented or reduced.

Furthermore, according to the method for producing the permeable adhesive tapes according to the invention, the permeable adhesive tapes having the properties described above can be produced easily and conveniently.

Claims (11)

1. A permeable adhesive tape comprising: a porous or permeable underside, a pressure-sensitive adhesive layer made of a natural rubber base, a synthetic rubber base or a pressure-sensitive acrylic adhesive and a release liner in that order, wherein the pressure-sensitive adhesive layer has permeable pores; containing elastic microspheres. 2. Permeable adhesive tape according to claim 1, characterized in that the elastic microspheres are contained in all or part of the permeable pores to such an extent that the elastic microspheres do not damage the permeability. 3. Permeable adhesive tape according to claim 1, characterized in that the elastic microspheres are present in an amount of 0.01 to 5.0 parts by weight in 100 parts by weight of the pressure-sensitive adhesive (expressed as solid content). 4. Permeable adhesive tape according to claim 1, characterized in that the elastic microspheres have an average particle diameter of 10 to 100 µm. 5. Permeable adhesive tape according to claim 1, characterized in that the elastic microspheres are non-hollow elastic microspheres or hollow elastic microspheres. 6. Permeable adhesive tape according to claim 1, characterized in that the hollow elastic microspheres are expanded hollow elastic microspheres. 7. Permeable adhesive tape according to claim 1, characterized in that the permeable adhesive tape is wound on a roll. 8. A method of making a permeable adhesive tape comprising: dispersing non-hollow elastic microspheres, hollow elastic microspheres or expandable microspheres homogeneously in a permeability-imparting agent to produce a first dispersion, dispersing the first dispersion in a solution of pressure-sensitive adhesive to which a cross-linking agent has been optionally added to form a second dispersion, Applying the second dispersion to a release liner, followed by drying while converting the expandable microspheres, if used, into hollow elastic microspheres, thereby forming the pressure-sensitive adhesive layer having permeable pores containing non-hollow elastic microspheres or hollow elastic microspheres, and then Laminating the porous bottom or a permeable bottom to the pressure-sensitive adhesive layer. 9. A process according to claim 8, characterized in that the expandable microspheres have an average particle diameter of 5 to 30 µm and drying is carried out at 80 to 200 ° C for 0.5 to 5 minutes, whereby the expandable microspheres expand and are converted into hollow elastic microspheres. 10. A method of making a permeable adhesive tape comprising: dispersing non-hollow elastic microspheres, hollow elastic microspheres or expandable microspheres in a system in which a permeability-imparting agent and optionally a cross-linking agent are homogeneously dispersed in a solution of a pressure-sensitive adhesive, Applying the dispersion to a release liner, followed by drying while converting the expandable microspheres, if used, into hollow, elastic microspheres, forming a pressure-sensitive adhesive layer having permeable pores containing non-hollow elastic microspheres or hollow elastic microspheres, and then Laminating a porous backing or a permeable backing to the pressure-sensitive adhesive layer. 11. A process according to claim 10, characterized in that the expandable microspheres have an average particle diameter of 5 to 30 µm and that drying is carried out at 80 to 200 ° C for 0.5 to 5 minutes, whereby the expandable microspheres are expanded so that they are converted into hollow elastic microspheres.